MEMS microphones typically are housed within a package interior and controlled by an adjacent integrated circuit chip. The package thus must have a footprint that is large enough to hold both the microphone chip and the integrated circuit chip. In addition, MEMS devices, such as MEMS microphones chips, often have extremely clean microstructure surfaces. Such clean microstructure surfaces, however, can stick together if they come into contact. When the surfaces remain stuck together, the device often is inoperable. This concept of surface sticking is known in the art as “stiction.”
A number of different factors can contribute to or cause stiction. For example, among other things, stiction may occur during wet release of a movable MEMS microstructure, where the surface tension of a draining rinse liquid can draw the microstructure into contact with an adjacent part, such as an underlying substrate or backplate (sometimes referred to as “release stiction”). Stiction also may occur to a MEMS microphone when mounting it (i.e., when mounting the package within which a MEMS microphone chip is mounted) to a printed circuit board. For example, flux/solder that secures the MEMS microphone to the circuit board may inadvertently contact the movable microstructure, causing stiction.